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Spark Plugs - Why are they burning different?

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Old Nov 12, 2010 | 03:08 PM
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Default Spark Plugs - Why are they burning different?
2011 Ultra Limited, SE 255 cams, adjustable push rods, SE AC, rinehart true duals, PCV and dyno. Replaced the plugs with NGK iridium and noticed front cylinder stock plug was burning dark...almost black and the rear cylinder plug was very very clean. After about 2 weeks, I pulled the NGKs and they were burning the same as stock. Bike runs good and performance is good...thoughts as to why the plugs would be so different in color...burning characteristics?? Thanks.
 
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Old Nov 12, 2010 | 03:17 PM
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Was told by a tuner that the front cylinder runs hotter than the back. That info is free and worth every penny. lol
 
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Old Nov 12, 2010 | 03:20 PM
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Need to see pictures. Does it look like the front plug has been burning oil?
 
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Old Nov 12, 2010 | 03:27 PM
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No, just looks like the front is richer than rear.
 
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Old Nov 12, 2010 | 03:44 PM
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It may be richer but shouldnt be. The rear cylinder is the one that usually gets hotter because it doesnt get the cool air that the front does while riding down the highway. That has no bearing on what the spark plugs look like or how rich or lean its running. Maybe you have an injector problem or a tuning problem.
 
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Old Nov 12, 2010 | 03:53 PM
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Default Plugs
Take her for a good run, then pull them out when she is still good and hot.Then compare.
 
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Old Nov 12, 2010 | 04:44 PM
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Rear cylinder head is hotter.

Rear combustion chamber is hotter

Rear plug burns cleaner cause it is hotter and front plug gets just a little soot

Bwana
 
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Old Nov 12, 2010 | 05:02 PM
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Default Sounds like a tuning issue
to me. I don't think this has much to do with the cylinder temps. Get a good tune done and I bet this becomes a non issue. The front cylinder is too rich and the rear is probably a little too lean. Just my .02 cents.
 
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Old Nov 18, 2010 | 07:31 PM
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mine does the same thing and i run a carb, i was told that the rear is cleaner because it runs hotter cause of air flow over engine
 
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Old Nov 18, 2010 | 07:34 PM
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Originally Posted by R.Rains
Take her for a good run, then pull them out when she is still good and hot.Then compare.
Do not pull your plugs out when they are hot. There is a chance you can pull out the threads from the head. Trust me, I've seen it happen.
 
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